Eucaryotic chromosomes are composed of DNA-protein fibers which are the loci of genes and gene regulatory systems. The structure and function of these systems may be related to the subunit structure which appears to underly chromatin fibers. Experimental evidence has supported the model that chromatin DNA and proteins are organized into a flexible chain of globular particles (given the name "nucleosomes"). This model will be tested and developed in the proposed research by measuring the dynamics, at the molecular level, of chromatin fibers prepared from avian erythrocytes. Rotational motion of "nucleosomes" in chromatin will be investigated by nanosecond fluorescence spectroscopy, using ethidium bromide as chromophore. The results of these experiments will be related to predictions of the chromatin subunit model.